Allow plugins to receive configuration from the nushell configuration (#10955)

# Description

When nushell calls a plugin it now sends a configuration `Value` from
the nushell config under `$env.config.plugins.PLUGIN_SHORT_NAME`. This
allows plugin authors to read configuration provided by plugin users.

The `PLUGIN_SHORT_NAME` must match the registered filename after
`nu_plugin_`. If you register `target/debug/nu_plugin_config` the
`PLUGIN_NAME` will be `config` and the nushell config will loook like:

        $env.config = {
          # ...
          plugins: {
            config: [
              some
              values
            ]
          }
        }

Configuration may also use a closure which allows passing values from
`$env` to a plugin:

        $env.config = {
          # ...
          plugins: {
            config: {||
              $env.some_value
            }
          }
        }

This is a breaking change for the plugin API as the `Plugin::run()`
function now accepts a new configuration argument which is an
`&Option<Value>`. If no configuration was supplied the value is `None`.

Plugins compiled after this change should work with older nushell, and
will behave as if the configuration was not set.

Initially discussed in #10867

# User-Facing Changes

* Plugins can read configuration data stored in `$env.config.plugins`
* The plugin `CallInfo` now includes a `config` entry, existing plugins
will require updates

# Tests + Formatting

- 🟢 `toolkit fmt`
- 🟢 `toolkit clippy`
- 🟢 `toolkit test`
- 🟢 `toolkit test stdlib`

# After Submitting

- [ ] Update [Creating a plugin (in
Rust)](https://www.nushell.sh/contributor-book/plugins.html#creating-a-plugin-in-rust)
[source](https://github.com/nushell/nushell.github.io/blob/main/contributor-book/plugins.md)
- [ ] Add "Configuration" section to [Plugins
documentation](https://www.nushell.sh/contributor-book/plugins.html)

src/tests/test_config.rs

@@ -1,4 +1,4 @@
-use super::run_test_std;
+use super::{fail_test, run_test_std};
 use crate::tests::TestResult;
 
 #[test]
@@ -100,3 +100,25 @@ fn mutate_nu_config_nested_filesize() -> TestResult {
         "kb",
     )
 }
+
+#[test]
+fn mutate_nu_config_plugin() -> TestResult {
+    run_test_std(
+        r#"
+            $env.config.plugins = {
+                config: {
+                  key1: value
+                  key2: other
+                }
+            };
+            $env.config.plugins.config.key1 = 'updated'
+            $env.config.plugins.config.key1
+        "#,
+        "updated",
+    )
+}
+
+#[test]
+fn reject_nu_config_plugin_non_record() -> TestResult {
+    fail_test(r#"$env.config.plugins = 5"#, "should be a record")
+}